He and Sr isotopic constraints on subduction contributions to Woodlark Basin volcanism, Solomon Islands

Journal Article · Thu Feb 01 04:00:00 EST 1990 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(90)90332-F· OSTI ID:7188924

Trull, T W; Kurz, M D ^[1]; Perfit, M R ^[2]

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1. Woods Hole Oceanographic Institution, MA (USA)
2. Univ. of Florida, Gainesville (USA)

In order to assess the nature and spatial extent of subduction contributions to arc volcanism, Sr and He isotopic compositions are measured for dredged volcanic rocks from the Woodlark Basin in the western Pacific. {sup 87}Sr/{sup 86}Sr ratios increase geographically, from ocean ridge values (.7025-.7029) at the Woodlark Spreading Center to island arc ratios (.7035-.7039) in the Solomon Islands forearc, with intermediate values near the triple junction where the Woodlark Spreading Center subducts beneath the Solomon Islands. {sup 3}He/{sup 4}He ratios are also more radiogenic in the forearc (6.9 {plus minus} .2 R{sub a} at active Kavachi volcano) than along the spreading center, where values typical of major ocean ridges were found (8.2 - 9.3 R{sub a}). Very low {sup 3}He/{sup 4}He ratios occur in many triple junction rocks (.1 to 5 R{sub a}), but consideration of He isotopic differences between crushing and melting analyses suggests that the low ratios were caused by atmospheric (1 R{sub a}) and radiogenic ({approx} 0.2 R{sub a}) helium addition after eruption. Variations in unaltered, magnetic {sup 3}He/{sup 4}He, and {sup 87}Sr/{sup 86}Sr ratios are best explained by subduction-related fluid or silicate melt contributions to the magma source region, perhaps from ancient Pacific lithosphere. However, mantle volatiles dominate the generation of Woodlark Basin rocks despite extensive subduction in the region.

• OSTI ID: 7188924
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Journal Name: Geochimica et Cosmochimica Acta; (USA) Journal Issue: 2 Vol. 54:2; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ALKALINE EARTH ISOTOPES
CHEMISTRY
GEOCHEMISTRY
GEOLOGIC STRUCTURES
HELIUM ISOTOPES
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
MAGMATISM
PACIFIC OCEAN
PETROGENESIS
ROCKS
SEAS
SEDIMENTARY BASINS
STRONTIUM ISOTOPES
SUBDUCTION ZONES
SURFACE WATERS
VOLCANIC REGIONS
VOLCANIC ROCKS